Television antenna



Feb. 24, 1942. H. R. LUBCKE 2,274,149

I TELEVISION ANTENNA Filed Oct. 25, 1941 FIG. 2.

I: 3 E B2 (0 FIG. 7.

FREQUENCY, MEGACYCLES WITNESSES: INVENTOR.

FIG. 5.

Patented Feb. 24, 1942 2,274,149 TELEVISION ANTENNA Harry R. Lubcke,Hollywood, Calif., assignor to Don Lee Broadcasting System, Los Angeles,Calif., a corporation of California Application October 25, 1941, SerialNo. 416,435

12 Claims.

This invention relates to broad-band antennas, particularly for use withultra-high frequency waves and for applications where such waves extendover a considerable frequency spectrum, as in television.

An object of this invention is to provide an antenna responsive to arelatively broad frequency spectrum.

Another object of this invention is to provide an antenna having maximumradiation if used for transmission, or maximum efliciency ofinterception if used for reception, in a horizontal plane. It is wellknown that this type of space pattern is desired; in almost everyantenna application.

.Still another object of this invention is to provide a strongmechanical structure, with certain antenna elements acting as structuralelements.

Still another object of this invention is to provide means wherebyconsiderably different radiation patterns may be obtained by mechanicaladjustment of the elements.

Still-another object of this invention is to provide a broad-bandantenna having a small yalue of wind resistance.

Still another object of this invention is to provide a broad-bandantenna of relatively simple and compact structure yet having a highvalue of effectiveness (so-called gain) A final object of this inventionis to provide an antenna system having broad-band impedance matchingcharacteristics to the necessary feeder lines to the transmitter orreceiver.

The ways in which these objects are attained are shown in connectionwith the accompanying drawing in which:

Fig. 1 shows a plan view of the antenna.

Fig. 2 shows a front elevation of the same.

Fig. 3 shows a representative polar coordinate graph of the energydistribution in a horizontal plane as radiated by the antenna when usedfor transmitting. The sensitivity in intercepting electromagnetic wavesfollows, of course, the same pattern when the antenna is used forreceiving. Y

Fig. 4 shows a rectangular coordinate graph of the bandwidth of theantenna.

Fig. 5 shows a plan view of an alternate arrangement of radiatingelements.

Fig. 6 shows a plan view of a second alternate arrangement of radiatingelements.

Fig. 7 shows a front elevation view of an alternate means of connectingthe feeder lines to the antenna. In meeting the need for a widefrequency band antenna I have experimentally determined that the energyresponse vs. frequency characteristic of an antenna element isproportional to the cross-sectional surface area of the conductor.

For instance, at a mean carrier frequency of 53 megacycles, the band offrequencies over which the response of one paddlewheel element I, Fig.1, is within 16% of the maximum valueis 5.7 megacycles. correspondingly,the bandwidth of a 1 inch diameter tubing element (not having thefan-like ends) is 3.8 megacycles. Further, the bandwidth of a inchdiameter element (without ends) is 2.2 megacycles. A wire, of evensmaller cross-section has a narrower bandwidth, but this is of littleinterest here because of structural considerations.

Since the present standards for television transmission call for abandwidth of 4.75 megacycles without substantial variation of response,the element I will be seen to be ideally suited for televisiontransmission antennas. For this purposev the paddles are 9" wide at theends,

. 32" long, and- 1%" thick, being supported in the center by a 11 3"outside diameter section of tubing. It is to be understood that this andsubsequent recitations of dimensions do not restrict this invention, butthat wide variations of bandwidth, and operating frequency may beobtained according to the teaching of this specification.

The configuration in which four of the above described elements arearranged I call reflected double-stack and is shown in Figs. 1 and 2.Ele-- ments l and 2 are disposed one above the other a half-wavelengthapart. Energy is conveyed from one to the other element by thestructural- 1y strong and electrically matched transposed pair ofconductors 3 and 4. These are everywhere equally distant from each otherand curve sensitivity in reception are obtained in a horizontal plane.Elements I and 2 are disposed at an angle of 25 degrees one to the otherin this embodiment for field-pattern reasons disclosed later.

Conductors 3 and 4 may conveniently be I formed of duraluminum pipe, asmay the centralportions of elements I, 2, 5 and 6. In this eventduraluminum screw thread elbows may be used to form the right angle bendat the top of conductor 3 to the right hand side of element 2, etc., andsimilar T's used at the lower junction of conductor 3 with element I andconductor II. Split blocks of an insulator such as mycalex or Bakelite(not shown) may be used to clamp conductors 3 and 4 at a fixed distanceapart at several points throughout the length thereof.

Elements 5 and 6 are each disposed wavelength -behind elements I and 2,respectively. This causes cancellation of the waves emitted into spacebehind elements 5 and 6 consequent reinforcement of waves emitted infront of elements I and 2. Waves emitted into space above and below thegroups of elements I and 5, 2 and 6 are partially cancelled in addition,the energy being emitted with maximum intensity in the horizontal plane.

The distribution of energy in the horizontal plane is shown in Fig. 3 inpolar coordinates. This is a curve plotted from field-strengthmeasurements made at a five mile radius from an operating televisionstation. The orientation of the curve is the same as that of Fig. 1. Thereduction of radiation of energy behind elements 5 and 6 and theincrease in front of elements I and 2 postulated above is seen to beborne out in fact.

This type of energy distribution is usually desirable, since it is arare occurrence that an ultrahigh frequency transmitter is located inthe center of the population it serves. High mountains are usually foundat one side of the city and high buildings likewise, since the betterclass residential district is the prime service area of suchtransmitters.

The radiation pattern of Fig. 3 may be altered by changing the relativemechanical positions of the elements. The staggering of pairs ofelements I and 5. 2 and 6 by degrees was for the purpose of obtaining anappreciable radiation behind elements 5 and 6 to serve a small populatedarea in that direction. By aligning all elements, as shown in Fig. 5,the rear radiation drops to a small value and the maximum frontradiation is symmetrical with respect to the axis perpendicular to thelength of the elements.

.Similarly, in Fig. 6, is shown an alternate arv This arrangementresults in a radiation pattern similar to Fig. 3 except on a greaterangle to the axis and somewhat greater radiation transverse thereto.

In the configurations described, certain dimensions were found to beoptimum. These are given below in order to fully describe thisinvention. It is to be understood; however, that they apply to a meanfrequency of 53 megacycles and will be proportionately different fordifferent frequencies of operation. 1

The separation between elements I and 2 was found to be uniformly 111inches. This is a half wavelength at the frequency of operation and wasthe optimum dimension for maximum fieldstrength in a horizontal plane.polarization of the emitted waves this dimension is vertical, with theelements laying in horizontal planes.

The separation of elements I and 2 from ele ments 5 and 6 has an optimumvalue of 40" for mitter feeder system. but are parasitically excited byradiant energy from elements I and 2.

The length of the driven elements I and 2 is 90" for 53 megacycles, orwavelength for all embodiments. The length of the parasitic elements 5and 6 however varies for each embodiment. For the configuration of Fig.1 this is /2 wavelength, for Fig. 5 (elements 8) this is slightly lessthan 1 5' wavelength, and for Fig. 6 (elements I0), slightly more than1; wavelength.

In any antenna installation the useful energy must be either conveyed tothe antenna from the transmitter or conveyed from the antenna to areceiver. In the present invention this is accomplished by an impedancmatching section II and I2 and feeders I3 and I4.

Each part II and I2 is one-quarter wavelength long and of across-sectional surface area approximately three times as great as theconductors 3 and 4, the latter being somewhat over one inch for thefrequency of 53 megacycles. Parts II and I2 are arranged to hingetogether or apart like two doors to allow exact adjustment of the1mpedance match. This adjustment varies the characteristic impedance ofthe matching section and is a convenient means by which to match theimpedance of the antenna structure I, 3, 4, to the feeders I3 and I4.The impedanccs of the latter are conveniently ohms for each line, thusthe impedance presented to the lower end of the matching section is 140ohms. The inner conductors I5 and I6 are connected to the matchingsection. Parts II and I2 may also be arranged for adjustment by atranslating motion mutually together and apart.

I have found that the most important condition to be met in the properfunctioning of this antenna assembly is that the two outer conductors I3and I4 be close together physically and that a good electrical bond llbe provided between the two. This bond may be attached to an electricalground, if available, thus allowing the structure to be firmly based ona tower or other grounded structure. The top and bottom of parts II andI2 may be similarly attached by means of insulators. Mechanical supportsfor the parasitic elements 5 and 6 have not been shown for sake ofclarity, but these may also be held by insulators attached to supportspreferably above the top of the upper elements and below the lowerelements, respectively.

In addition to the arrangement shown in Fig. 2 the antenna may be fedaccording to Fig. 7. Conductors 3 and 4 are attached to an unbrokenradiating element I. The spacing between adjacent surfaces throughout thlength of these I conductors in either figure is approximately one- Forhorizontal 53 megacycles. or 1% wavelength for all embodiments.

The elements 5 .and B have no metallic conhalf of the radius thereof. InFig. 7, however, the inner conductors I5 and I6 of the feeders I3 and I4are spaced outward in joining the element I and increase incross-sectional area from the usual '70 ohm dimension at the juncturewith I3 and I4 to approximately the element dimension at the element.This maintains the characteristic impedance substantially constant andthe inner conductors are attached to the element at a physicalseparation corresponding to this value.

Another essential characteristic of the antenna is the frequencyresponse shown in Fig. 4. This is the overall characteristic of matchingsection and antenna with the radiated fieldstrength determined with alinear rectifier intercepting the emitted'energy at a considerabledistance from the structure. Two desirable characteristics are noted;first, the response is uniform over a wide band of frequencies, andsecond, that the response drops to a small value beyond this band offrequencies, particularly on the low frequency side. The latter greatlyaids, if not largely accomplishes, the function of a single sidebandfilter as used in television transmission practice.-

This operation has been proven by the continued use ofthe antennastructure in regularly scheduled television broadcasts. For thisapplication the carrier frequency is conveniently located between 51 and52 megacycles. 7

Finally, the measured field-strength gain of this antenna over the usualreference half-wave antenna is 5.5. That is, a given amount of power fedto this antenna will result in 5.5 times the field-strength voltageobtained over the service area as would be obtained were the same powerfed to a single half-wave antenna.

Thus far, the considerations have been for horizontally polarized waves.It is evident to those skilled in the art that the antenna structure maybe utilized for emitting or intercepting vertically polarizedelectromagnetic wave energy by turning the whole assembly through 90degrees in the vertical plane so that the radiating elements I, 2, and 6are vertical. The alignment of the elements as shown in Fig. 5 ispreferable. Since the vertical as well as horizontal radiation patternis substantially the same as shown in Fig. 3 the same performance over aservice area will be secured.

In considering the wind resistance of this antenna it is evident that itis of small value because of the flattened cross-section of thebroadband radiating elements. For horizontal polarization, the majordimension of the cross-section is horizontal, as shown in Figs. 1 and 2.The projected area exposed to the wind is thus a minimum in relation tothe external surface effective in producing a broad-band electricalcharacteristic. For vertical polarization, the paddles" may be set togive the minimum pro jected area in the direction of prevailing strongwinds in any locality. While the antenna described comprised two pairsof element spaced a half-wavelength apart, it will be understood thatthe same construction may be duplicated to produce three or more pairssimilarly successively spaced, or stackedff In consideringcross-sectional areas of elements and conductors in this specificationit is the external surface of such areas which is of importance; thecenter being hollow according to recognized practice to give a favorablestrength to weight ratio. Also, the cross-sectional areas need not becircles and ellipses, but may be squares and rectangles, etc.

It will be noted in Figs. 1 and 2 that elements I and 2, have been shownas separated into two halves by connection to conductors 3 and 4. Thisis preferable in this embodiment. However, from the standpoint ofelectromagnetic radiation, I and 2'may be considered as an unbrokenmetallic surface. thus an element approximately a halfwavelength inlength. 7 Having thus fully described my invention, I

claim:

1. A broad-band antenna system comprising; a group of radiating elementshaving a greater cross-sectional surface area at the extremities than atthe center thereof, said elements being approximately one-halfwavelength long, spaced approximately parallel one-half wavelengthother; and a second group of similar elements similarly spaced and notconductively coupled one to the other, located approximatelythreesixteenths wavelength from the first said group.

.2. A broad-band antenna system comprising;

a plurality of radiating elements having a greater cross-sectionalsurface area at the extremities than at the center thereof, saidelements being approximately one-half wavelength long, spacedapproximately parallel one-half wavelength apart, and being conductivelycoupled one to the other such that one-half of one-half-wave element isconnected to the opposite half of the succeeding half-wave element; anda second plurality of similar elements similarly spaced and notconductively coupled one to the other, located approximatelythree-sixteenths wavelength from the first said plurality.

3. A broad-band antenna system comprising; a plurality of radiatingelements having a greater cross-sectional surface area at theextremities than at the center thereof, said elements beingapproximately one-half wavelength long, spaced approximately parallelone-half wavelength apart, and being conductively coupled one to theother such that one half of one half-wave element is connected to theopposite half of the succeeding half-wave element; and a secondplurality of similar elements similarly spaced and not conductivelycoupled one to the other located approximately in a plane parallel toand spaced approximately three-sixteenths'wavelength from the first saidplurality.

4. A broad-band antenna system comprising; a plurality of radiatingelements having a greater cross-sectional surface area at theextremities than at the center thereof, said elements beingapproximately one-half wavelength long, spaced approximately parallelone-half wavelength apart, and being conductively coupled one to theother such that one half of one half-wave element is connected to theopposite half of the succeeding half-wave element; and a secondplurality of similar elements similarly spaced and not conductivelycoupled one to the other, located approximately three-sixteenthswavelength from said plurality, successive pairs of each pluralitylaying in planes at an angle to the preceding I pair of saidpluralities.

apart, and being conductively coupled one to the 5. A broad-band antennasystem comprising; a plurality of radiating elements having a greatercross-sectional surface area at the extremities than at the centerthereof, said elements being approximately one-half wavelength long,spaced approximately parallel one-half wavelength apart, and beingconductively coupled one to the .other such that one half of onehalf-wave element is connected to the opposite half of the succeedinghalf-wave element; and a second plurality of similar elements similarlyspaced and not conductively coupled one to the other, locatedapproximately three-sixteenths wavelength from said plurality,successive pairs of each plurality laying in planes at an angle of theorder of fortyfive degrees to the preceding pair of said pluralities.

6. A broad-band antenna system comprising; a plurality of radiatingelements having a greater cross-sectional surface area at theextremities than at the center thereof, said elements beingapproximately one-half wavelength long, spaced one-half wavelength apartwithsuccessive elements of the plurality contained in planesintersecting at an angle of approximately twenty-five degrees, and beingconductively coupled one to the other such that one'half of onehalf-wave element is connected to the opposite half of the succeedinghalf-wave element; and a second plurality of similar elements similarlyspaced and not conductively coupled one to the other, each locatedapproximately three-sixteenths wavelength from an element of the firstsaid plurality.

7. A broad-band antenna system comprising; a group of radiating elementshaving a greater cross-sectional surface area at the extremities than atthe center thereof, said elements being approximately four-tenthswavelength long spaced approximately parallel one-half wavelength apart,and being conductively coupled one to the other; and a second group ofsimilar elements approximately one-half wavelength long similarly spacedand not conductively coupled one to the other located approximatelythree-sixteenths wavelength from the first said group.

8. A broad-band antenna system comprising; a stack of radiating elementshaving a, greater cross-sectional surfacearea at the extremities than atthe center thereof, said elements being approximately four-tenthswavelength long, stacked one-half wavelength apart, and beingconductively coupled one to the other; and a second stack of similarelements approximately seven-sixteenths wavelength long, notconductively coupled one to the other, located approximatelythree-sixteenths wavelength from the first said stack and at an anglethereto.

9. A broad-band antenna system comprising; a plurality of radiatingelements having a greater cross-sectional surface area at theextremities than at the center thereof, said elements beingapproximately one-half wavelength long, spaced approximately parallelone-half wavelength apart, and being conductively coupled one to theother by conductors of substantial mechanical rigidity spaced surface tosurface less than the radius thereof apart, such that one half of onehalf-wave element is connected to the opposite half of the succeedinghalf-waveelement; and a second plurality of similar elements similarlyspaced and not conductively coupled one to the other, each locatedapproximately three-sixteenths wavelength from an element of the firstsaid plurality.

10. A broad band antenna system comprising; a stack of radiatingelements having a greater cross-sectional surface area at theextremities than at the center thereof, each element bein slightly lessthan one-half wavelength long and stacked one-half wavelength apart;conductors of substantialmechanical rigidity positioned adjacent-one tothe other, connecting said elements of said stack; conductors of greatersurface area one-fourth wavelength long connected at one extremity tothe junction of an element and said first conductors; and feeders forconveying radio frequency energy to said system connected at the otherextremity of said conductors of greater surface area. 7

11. A broad-band antenna system comprising; two radiating elementsslightly less than onehalfwavelength long spaced one-half wavelength inapproximately a common plane, two conductors connecting said elements,the conductors positioned adjacent one to the other, such that one-halfof one element is connected to the other half of the second element; two

conductors one-quarter wavelength long of greatconductor; a pair ofcoaxial feeders, the inner conductors thereof connected to the otherextremity of said conductors of greater cross-sectional surface and theouter conductors thereof connected together; two more radiating elementsapproximately one-half wavelength long located in approximately a commonplane and approximately three-sixteenths wavelength from said firstcommon plane.

12. A broad-band antenna system comprising; a stack of radiatingelements having a greater cross-sectional surface area at theextremities than at the center thereof, each element being slightly lessthan one-half wavelength long and stacked one-half wavelength apart;conductors of substantial mechanical rigidity positioned closelyath'acent one to the other, connecting said elements of said stack;feeders for conveying radio frequency energy to said system having innerand outer conductors, a conductor connecting said outer conductors atthe extremities thereof, said inner conductors extending beyond saidouter conductors, and increasing in cross sectional surface areaapproximately proportional to said extension and connecting to anelement of said' stack.

, HARRY R. LUBCKE.

